Microelectronic devices generally comprise a thin slab of a semiconductor material, such as silicon or gallium arsenide, commonly called a die or a semiconductor chip. Semiconductor chips are commonly provided as individual, prepackaged units. The active circuitry is fabricated in a first face of the semiconductor chip (e.g., a front surface). To facilitate electrical connection to the active circuitry, the chip is provided with bond pads on the same face. The bond pads are typically placed in a regular array either around the edges of the die or, for many memory devices, in the die center. The bond pads are generally made of a conductive metal, such as copper or aluminum that is approximately 0.5 microns (μm) thick. The bond pads could include a single layer or multiple layers of metal. The size of the bond pads will vary with the device type, but will typically measure tens to hundreds of microns on a side.
Semiconductor chips are commonly provided in packages that facilitate handling of the chip during manufacture and during mounting of the chip on an external substrate such as a circuit board or other circuit panel. For example, many semiconductor chips are provided in packages suitable for surface mounting. Numerous packages of this general type have been proposed for various applications. Most commonly, such packages include a substrate, commonly referred to as a “chip carrier” with terminals formed as plated or etched metallic structures on the dielectric. These terminals typically are connected to the contacts of the chip itself by features such as thin traces extending along the chip carrier itself and by fine leads or wires extending between the contacts of the chip and the terminals or traces. In a surface mounting operation, the package is placed onto a circuit board so that each terminal on the package is aligned with a corresponding contact pad on the circuit board. Solder or other bonding material is provided between the terminals and the contact pads. The package can be permanently bonded in place by heating the assembly so as to melt or “reflow” the solder or otherwise activate the bonding material.
Despite the various improvements made in the art, further improvements would be desirable in the case of multi-chip packages, particularly for chips having contacts located in central regions of the chips. Certain semiconductor chips, such as some memory chips, are commonly made with the contacts in one or two rows located in a central region of the chip.